1. Field of the Invention
This invention relates to an information recording-reproducing method and apparatus, and in particular, to an information recording-reproducing method and apparatus in which error correction is effected.
2. Related Background Art
Various information recording mediums such as disk-like mediums, card-like mediums and tape-like mediums are known as information recording mediums on which information is recorded by the use of light and from which recorded information is read out. Among these, an optical information recording medium formed in the shape of a card (hereinafter referred to as the optical card) is expected to have a great demand as a compact, light-weight information recording medium of great capacity that is convenient to carry.
FIG. 1 of the accompanying drawings is a schematic plan view of such an optic card, and FIG. 2 of the accompanying drawings is a fragmentary enlarged view thereof.
In FIG. 1, reference numeral 1 designates the optical card, reference numeral 2 denotes information tracks, and reference numeral 3 designates the home position. The optical card 1 is such that by scanning a light beam modulated in accordance with recording information and reduced to a minute spot on the optical card, information is recorded as optically detectable record bit rows (information tracks). To accurately record and reproduce the information at this time, without causing trouble such as crossing of the information tracks 2, it is necessary to control the applied position of the light beam in a direction perpendicular to the scanning direction (auto-tracking, hereinafter referred to as AT). Also, to stably apply the minute spot in spite of any bending or mechanical error of the optical card, it is necessary to control the light spot in a direction perpendicular to the optical card (auto-focusing, hereinafter referred to as AF). As shown in FIG. 2, tracking tracks 5 (5.sub.1, 5.sub.2, . . . ) for effecting AT are provided between the information tracks 2 (2.sub.1, 2.sub.2, . . . ) of the optical card 1.
A method of recording information on and reproducing information from the optical card will now be described.
In FIG. 1, the light beam exists at the home position 3 at first. The light beam then moves in the direction of arrow D, seeks an information track 2N to be recorded or reproduced, and scans the information track 2N in the direction of arrow F, thereby accomplishing recording or reproducing of the information.
Also, when the optical information recording medium is a nonerasable postscript type recording medium, the recorded data is immediately reproduced and whether it is the same as the record data is examined (hereinafter referred to as verify), and if the result is wrong, a recording method of recording the data again on the next information track is performed.
As means for examining whether the data recorded on the recording medium is the same as the record data, i.e., verifying means, there is adopted a method of comparing the record data with the immediately reproduced data of the recorded data and examining any error in the data, or a method of comparing the parity of the record data with the parity of the reproduced data to thereby examine any error in the data.
However, in such methods, when the information recording medium is reproduced after verification of the record, there is a possibility that error occurs due to dust, a flaw or the like. Usually, such a recording-reproducing apparatus has a correcting ability to add an error correction code (ECC) to the data to be recorded and to correct the error resulting from such dust, flaw or the like on the information recording medium during recording and reproduction. However, in the above-described methods, the error correcting ability during verification is the same as the error correcting ability during reproduction. This has led to a problem that there occurs a case wherein correction is impossible during reproduction with regard to an error due to an error cause (dust, a flaw or the like) newly arising after recording and verification.
So, U.S. Pat. No. 3,774,154 proposes an apparatus in which the error correcting ability is reduced more during verification than during reproduction, whereby even an error arising after verification can be corrected. This apparatus has two error correcting means, i.e. ECC and a signal error pointer. The apparatus is designed to display a recording error when an error exceeding the ability of the ECC is detected during verification. Also, in column 5, lines 48 through 64 of the above-noted U.S. Patent, it is disclosed that the criteria of light check are reduced during verification.
However, the above-described apparatus is complicated in construction, because it has means for generating a signal error pointer, in addition to ECC.